1. Field of the Invention
The present invention relates to an abnormality detection apparatus and an abnormality detection method for an internal combustion engine, and particularly relates to an abnormality detection apparatus and an abnormality detection method for an internal combustion engine to be applied to a motive power output apparatus provided with a plurality of power sources including the internal combustion engine.
2. Description of the Background Art
Conventionally, as an abnormality detection apparatus for an internal combustion engine that detects an abnormal cylinder where explosive combustion is not performed due to clogging or failure of a fuel injection valve, for example, Japanese Patent Laying-Open No. 02-49955 discloses a cylinder abnormality detection apparatus for an internal combustion engine that detects rotation angular speed of a crankshaft serving as an output shaft of the internal combustion engine by synchronizing with a combustion process of each cylinder, and detecting an abnormal cylinder causing irregular misfire based on a deviation between the detected rotation angular speed and a reference value of the angular speed.
According to the above, when a difference between rotation speed of a targeted cylinder and rotation speed of the previous cylinder serving as the reference value is larger than a predetermined value, the cylinder abnormality detection apparatus for the internal combustion engine sets a reference value for determining the next rotation speed to a value larger than the rotation speed by the predetermined value. Therefore, while an abnormality is caused in any cylinder and even in a case where accidental misfire is caused in a cylinder where an explosion process is performed immediately before the cylinder, it is possible to precisely determine that the cylinder where an abnormal state is intermittently caused has the abnormality.
However, in a case where the cylinder abnormality detection apparatus disclosed in Japanese Patent Laying-Open No. 02-49955 is applied to a hybrid vehicle of a mechanically split type, there is a problem that the abnormality of the internal combustion engine cannot be precisely detected due to the following reason.
In a hybrid vehicle provided with an internal combustion engine and a motor generator as power sources, a crankshaft of the internal combustion engine, a rotation shaft of the motor generator and a drive shaft may be mechanically connected via a planetary gear. It should be noted that the planetary gear has a property where, when rotation speed and torque (hereinafter, both are collectively called as a rotation state) of two out of the three rotation shafts mentioned above are determined, a rotation state of the remaining rotation shaft is inevitably determined.
In a hybrid vehicle having such a configuration, motive power output from the internal combustion engine is split into motive power to be mechanically transmitted to the drive shaft and motive power to be regenerated as electric power. Further, by running the motor generator with using the regenerated electric power, the vehicle can travel while outputting desired motive power. Since the motive power of the motor generator can be output from the drive shaft, the vehicle can also travel with only using the motive power output from the motor generator.
That is, in the hybrid vehicle, the crankshaft of the internal combustion engine and the rotation shaft of the motor generator are connected so as to be rotated at relative but different rotation speed from each other. Therefore, the rotation state of the motor generator largely influences the rotation angular speed of the crankshaft of the internal combustion engine.
However, the conventional cylinder abnormality detection apparatus for detecting the abnormal cylinder based on the rotation angular speed of the crankshaft is to be applied to the motive power output apparatus having only the engine as the power source, and hence such an influence of the motor generator over the rotation state of the crankshaft is not taken into consideration. As a result, the internal combustion engine does not easily estimate torque actually generated in accordance with a combustion state thereof with high accuracy. Therefore, there is a problem that the abnormal cylinder of the internal combustion engine cannot be precisely detected.